Official University of Virginia sports documents explain that Washington and Lee baseball fans first called University of Virginia players "a bunch of rowdy Wahoos," and used the "Wahoowa" yell as a form of derision during the in-state baseball rivalry in the 1890s, presumably after hearing them yell or sing "wa-hoo-wa ...
Their fight song is also to the tune of Auld Lang Syne. So there's that too....